Composite nanometal particles of ultrafine particles are developed as an electroconductive metal paste material that it is possible to be sintered with electroconductive material at low temperature in addition to high strength and superior electroconductivity and thermal conductivity, and in Japanese patent No. 4680313 (patent document 1), a part of the present inventors disclose the composite nanosilver particle. The composite nanosilver particle described in the patent document 1 has the organic coating layer derived from alcohol and contains metal ingredient in large quantities due to the considerable increasing of the silver core weight in comparison with conventional one.
However, in the nanometal particle comprising the composite nanometal particle having the organic coating layer or the noble metal, since it is difficult to perform mass-production and raw materials are expensive, the manufacturing cost of the metal paste containing the composite metal particle in large quantities increases, so that the application does not always progress.
As a method to solve such a problem, there is a trial in which metal pastes is developed by mixing the nanometal particle and the conventional metal particle. In Japanese Patent Laid-Open No. H7-320535 (patent document 2), it is described the electroconductive paste comprising metal ultra-fine particles such as silver, copper or copper-silver alloy and glass frit, where an average particle size of the metal ultra-fine particles exists in the range of 1 nm to 100 nm.
Furthermore, in Japanese patent No. 4600282 (Patent document 3), it is described the electroconductive paste containing metal powder comprising spherical type particle (A) in which an average particle diameter of primary particle is 0.1 to 1 μm and spherical type particle (B) in which average particle diameter of primary particle is not larger than 50 nm and said metal powder is selected among platinum, gold, silver, copper, nickel and palladium.
Average particle diameter is not s than 50 nm, and powder made up of silver fine particles including organic component and mean diameter are more than 50 nm, and, at Japanese Patent Laid-Open No. 2011-58041 bulletin (patent document 4), the paste which mixed powder made up of copper system fine particles including organic component with solvents is described. In patent document 4, the copper based fine particles also contain organic ingredient, and the silver based fine particles and the copper based fine particles are produced by the pyrolysis control method in absence of solvent under the presence of an amine compound. Namely, in the patent document 4, a commercial copper powder larger than micron size is not used, and a copper based fine particle of nano size to submicron size is produced by the method same as the silver based fine particle, and the particles has much organic ingredient.    [Patent Document 1] Japanese patent No. 4680313    [Patent Document 2] Japanese Patent Laid-Open No. H7-320535    [Patent Document 3] Japanese patent No. 4600282    [Patent document 4] J Japanese Patent Laid-Open No. 2011-58041